For example, JP-A-2010-114696 (PTL 1) discloses an electromagnetic wave transmission sheet having a mesh-like electrode, in which the length of a width perpendicular to a traveling direction of a transmitted electromagnetic wave is almost equal to a natural number multiple of half of the wavelength of the transmitted electromagnetic wave so as to be in a resonating state in a vertical direction.
In addition, JP-A-2005-317462 (PTL 2) discloses a plasma treatment device which includes a waveguide tube for electromagnetic wave distribution which propagates an electromagnetic wave therethrough, and a plurality of waveguide tubes for electromagnetic wave radiation branched from the waveguide tube for electromagnetic wave distribution and respectively provided with a plurality of slots. Further, a plurality of power supply windows make the waveguide tube for electromagnetic wave distribution be communicated with the respective waveguide tubes for electromagnetic wave radiation, and each power supply window is set such that an opening width increases in a direction toward the electromagnetic wave propagation direction side and such that a central axis parallel to the longitudinal direction of the waveguide tube for electromagnetic wave radiation is offset in the electromagnetic wave propagation direction side with respect to a central axis of a corresponding waveguide tube for electromagnetic wave radiation in a direction toward the opposite side of the electromagnetic wave propagation direction side.
In addition, JP-A-2002-280196 (PTL 3) discloses a plasma generating device in which a plurality of coupling holes are provided in waveguide tubes disposed in a plasma generating chamber, coupling factors of the coupling holes which are sequentially located toward the front end side of the waveguide tubes are increased one by one, and a plurality of dielectric windows corresponding to the respective coupling holes of the waveguide tube are provided in the plasma generating chamber. In addition, it is disclosed that an interval of the coupling holes is set to (2n+1)·λg/2, and an interval between a selected coupling hole and a short-circuited plate of the front end of the waveguide tube is set to λg/4. Here, λg is an in-tube wavelength of the waveguide tube, and n is an integer.